T Nation

Cardio and soreness

I think I know the answer to this, I just want to know what other people think. Is it ok to do cardio even if your legs are sore from a couple of days ago Leg workout?

Light to moderate cardio should be ok, but all out maximal interval work should be avoided. Lifting primarily targets the fast glycolytic and to some extent the fast oxidative glycolytic fibers and so will high intensity interval training. Light to moderate cardio focuses primarily on slow oxidative fibers and minimally recruits the other fibers, so it is ok.

There is no such thing as a glycolitic fiber, or a slow oxidative fiber.

Could you please explain further? Obviously, I don’t agree with your statement, but I would like to hear your rationale behind your statement. I have always preferred this terminology for differentiating muscle fibers as compared to type I, IIa, IIb or slow twitch/fast twitch. I prefer this terminology because it is a functional description of how different muscle fibers play different roles when it comes to metabolism.

I would really like to hear why you don’t agree with me, so I’m bumping this back up to the main page in hopes that you will see. I have used these muscle fiber descriptions now for years and I have seen them in textbooks, class lectures, journal articles and professional conferences. I would like to know the source of your information so that I can check it out myself. There is always controversy in the scientific world and I can’t keep up with everything as much as I try.

I think that the problem here is simply terminology. Glycolytic would be the type II fibers and slow oxidative would be the type I fibers.Mmmmmmmmkay?

I agree with you about terminology, but to say that something doesn’t exist just because that person has not heard of that terminology seems unlikely.

The informational sources I am familiar with and that I base my opinion on is a book called Human Anatomy and Physiology by Dr. Robert Killian PhD. As a nurse, who has a fair knowlege of human anatomy, I have never heard of anything such as a glyocolytic fiber. The process of glycolosis is the process of breaking down fat into usable energy (also known as the Krebs Cycle). It is a chemical process that does occur in the muscle fiber, but only in skeletal muscle (as opposed to involuntary muscles such as the heart and stomach, etc.). It occurs when the muscle is exerted to the point that there is a negative oxygen deficit and a build-up of lactic acid in the muscle. So, any skeletal (or voluntary muscle) is prone to the glycolytic process.

I might suggest that you pick up a recent textbook on exercise physiology. I’m not sure how much you deal with exercise physiology on the job, but as someone who posts on the forum, I assume that you’re interested in the topic. The nomenclature that I choose to use when describing different skeletal muscle fiber types is based on the physiology of the fibers rather than the anatomy. The anatomy of fibers does not tell you much other than the line of pull and the pennation pattern. Fast gylcolytic fibers (fast twitch) are fibers that do not contain significant amnounts of mitochondria, but have the capacity to generate energy via the creatine phosphate system and anaerobic glycolysis. These are the fibers primarily recruited during heavy lifting or activities like sprinting. Slow oxidative (slow twitch) fibers are chock full of mitochondrion and have the ability to use both fat and glucose as energy substrates via aerobic (oxidative) metabolism. Fast oxidative-glycolytic fibers have a little of both the aforementioned fibers. As a side note, glycolysis is the process of converting stored carbohydrate into energy (not fat). I do recognize though that the end product from both free-fatty acid and glucose is acetyl-coA which runs through the Krebs cycle. Glycolysis can occur both in oxidative and non-oxidative conditions. Of course, much more ATP can be produced via the oxidative process (as compared to the 2ATP garned from anaerobic glycolysis) once the glucose is converted to acetyl-coA and runs through the Krebs Cycle producing the proper substrates for oxidative phosphoralation via the electron transport shuttle. I think you get 32-33 or something like that. If you are in the market for a good textbook, McArdle, Katch and Katch’s Exercise Physiology is good and there is a more up to date book by somebody with a last name that starts with W. Williams maybe, but I don’t remember. It has a gray cover. If I come up with the name, I’ll post it here. Thanks for your response. If I can be of any further help, please ask.

I prefer Fox’s physiological basis for sport and exercise (Foss and Keteyian) rather than Mcardale,katch and Katch but your definiton of muscle fibres is spot on although the range of fibres can be broken down further as certain intermedate fibres exist between the type I, IIa and IIb classification that are commonly used that have the full spectrum of mixed oxidative and glycolitic potential. I would also be a bit wary of saying that a certain type of training affects a certain type of fibres, due to both the size principle (exluding ballistic activities) and the fibre type conversion that can occurdue to training.

I agree that it is very dangerous to talk about specific training styles which affect certain fiber types. I do agree that there is a significant amount of conversion with the type II glycolytic fibers. Specifically, I saw a presentation at an ACSM conference last November that talked about how training for max force and a maximal rate of force development (study was on elite Oly lifters) caused a significant shift of the type IIB fibers to type IIA. But, I think that it is safe to say that there is minimal conversion of the type I slow oxidative fibers to fast glycolytic or even intermediate fibers. Also, I think that the fast-glycolytic fibers are minimally recruited in any form of cardiovascular exercise kept under lactate threshold. As for the fast oxidative glycolytic fibers, these are much trickier and I think that where the majority of your training lies, so will these fibers. So to each their own goals.